Weighing sensor having a stop structure

ABSTRACT

A weighing sensor according to the principle of electromagnetic force compensation, wherein a stop is provided on the load receiver for a lever or a component carried by it.

FIELD OF THE INVENTION

The present invention relates to a weighing sensor with a monolithicconstruction, like those used for rotary filling heads or multiple-headscales.

BACKGROUND

Weighing sensors used for rotary filling heads are advantageouslyarranged in the shape of a circle, wherein an attempt is made to place amaximum of weighing cells on the smallest possible divided circle. Thiscircular arrangement of weighing sensors saves installation space.

In the beverage industry, rotary filling heads are known, for example,according to DE 20304296 U, in which numerous filling stations arearranged in a circle, and very high product throughputs can be achieveddue to the continuous filling. These filling machines have a fillinghead with a flow-rate controller, which apportions the desired quantityof fill material.

For free-flowing bulk goods, volume rotary filling heads are known. Thefilling head is pre-set according to the density of the fill materialand directs a constant volume into the corresponding filling container.The disadvantage of these filling systems lies in the variation indensity of the supplied products. Detergents can be fed, e.g., from thesilo or directly from the flocculation to the filling system, and thuscan have a different density due to the different pile heights.Furthermore, the construction of the volumetric filling heads limits thevolume ranges and thus the weight ranges of the fill material, i.e.,such systems can operate only with a limited measurement range.Volumetric rotary filling heads usually have a downstream check scale,which checks the fill weight of the packages and adjusts the fillinghead quantity accordingly. The disadvantage of these filling systemslies in the check weighing process, which is relatively far removed fromthe actual filling process and which is associated with greater waste ofproduct with incorrect weight due to the time lag of the downstreamcheck scale.

According to the state of the art, rotary filling heads are known whichare based on the DMS weighing technique. This shows the disadvantage ofthe long settling time of the DMS weighing cell upon load input. Thisproperty is amplified by the rotation of the entire filling head. Inaddition, DMS weighing cells exhibit deflection under increasing load,which must be corrected in the state of the art with, for example, anadditional correction cell (DE 372 78 66 C2).

For installation of the weighing technology in the head of a rotaryfilling machine with a basic circular construction, problems arise dueto the installation relationships of a measurement cell. Weighing cellsthat are common according to the state of the art have a cuboid housing.For introduction into a divided circle, one can see that the smallestpossible divided circle diameter is strongly limited by the geometricform of the measurement cell.

The weighing cells according to the state of the art shown in EP 1 409971 with a wide fixed linkage and a trapezoidal parallelogram guidanceare not suitable for accommodation in a divided circle.

EP 518202 B1 discloses a weighing sensor in which the individualfunctional units of the block system are implemented by means of thinsections. The figures show a weighing sensor with a narrow construction,but again there is the problem that the force-compensating magnet systemrepresents the greatest width of the system, and this lies opposite theload-receiving side as is known in the state of the art. The diameter ofthe divided circle is also here definitively defined by the magnetarrangement.

The length dimensions of the weighing cells produce anotherdisadvantage. The state of the art demonstrates weighing cells that havea parallelogram-guidance load receiver, wherein there are elasticlinkages between the upper and lower parallelogram arms that reduce themagnitude of an applied force. The state of the art here demonstratesdifferent weighing sensors with up to four force-converting stages,wherein systems with very high force-conversion ratios up to 1500:1 areto be found primarily in static applications.

The weighing sensors known according to the state of the art areconstructed with a compensation lever that is extended up to thecompensation system. In the case of electromagnetic force compensation,this is a system consisting of a coil and a permanent magnet system. Themagnet is arranged, as described, e.g., in DE 19923207 C1, behind theforce-reducing linkages. Among other things, the upper and lowerparallelogram arms for the moving load receiver are constructed on thefixed part.

For monolithic weighing systems manufactured by machining, the state ofthe art is represented by an arrangement of load receivers, forceconverting levers, stationary base elements, and magnet systems lyingspatially one behind the other. Furthermore, the state of the art showsus a magnet surrounded by block material, in order to achieve highmeasurement accuracy of the system. Such a system is not suitable for acircular arrangement with the goal of smallest possible diameter of thedivided circle. A construction with a magnet arranged between the twoparallelogram carriers (e.g., in DE 3243350 C2) can indeed have aspace-saving arrangement, but the lever principle and the limited forceconversion ratio of the system in this arrangement limits the use to avery limited weight range.

For suitability of a weighing sensor according to the principle ofelectromagnetic force compensation in a circular arrangement, theconstruction of the narrowest possible form for the weighing cell isessential. The disadvantage of such a construction lies in the weakeningof the Roberval-type linkages with respect to torsion perpendicular tothe introduction of force in the transverse direction of the blocksystem. From the state of the art, it is known that monolithic weighingsensors between the load receiver and the first lever (and the otherforce converting levers) are advantageously constructed with a couplingelement consisting of an intermediate bar and two thin sections.Furthermore, an advantageous design in the state of the art has involvedconstructing a thin section in the first coupling rod in thelongitudinal direction of the load receiver, in order to avoid torsionalmoments on the force converting lever. As an example here, thepublication EP 291 258 A2, especially FIG. 2, can be referenced.

The combination of narrow Roberval-type linkages (for forced parallelguidance of the load receiver) and the cited thin section leads to aless torsion-resistant weighing sensor in case of eccentric forceintroduction in the transverse direction of the block. Therefore, in EP1550849A2 it was mentioned to construct the parallelogram armsaccordingly wider than the block system, which represents a considerableadded expense relative to the original, primarily two-dimensionalweighing sensor.

DE 200 07 781 U1 discloses a weighing sensor with several forceconverting levers, in which a calibration weight can be selectivelylowered onto or raised from a lever section. As long as the calibrationweight is not being used, it can be pushed by mean of a separate liftingmechanism against the base element constructed as a stationary base,which then acts as a stop.

SUMMARY OF THE INVENTION

In view of the disadvantages named above, the solution is to create aweighing sensor which is constructed as short as possible (with respectto the distance between load receiver and stationary base).Simultaneously, the construction should be as narrow and compact aspossible and should provide a reliable, adequate force conversion ratiothat is largely free from interfering forces. In this way, a maximum ofweighing cells should be able to be provided on the smallest possibledivided circle for a circular arrangement.

The weighing sensor can be formed with an especially space-saving andshort construction if the load receiver has a stop for a lever of theforce converting mechanism. Alternatively or additionally, the stop canalso be provided for components of a force-compensation system or alsofor a compensation weight for at least partially compensating an initialload that is applied to the load receiver or that is intrinsic to thesystem. Such a stop according to the invention is especially helpful forthe case in which a lever construction is designed for a weighing sensorin such a way that the last lever in the direction of force flow extendsin the direction toward the load receiver.

For the compact configuration of the weighing sensor which can beachieved by the previously described lever guidance, a stop isadvantageously provided as overload protection for the last lever. Whilesuch a stop is constructed relative to the stationary base in the stateof the art, the weighing sensor presented here uses the load receiverinstead of the stationary base for forming the stop in the way accordingto the invention. This allows for the elimination of the preparation ofa solid-body section for such a stop, which simplifies the overallconfiguration. Instead, if there is an overload, the last lever oranother element arranged on this lever can strike against the loadreceiver or a stop part arranged on this load receiver, and thusover-extension of connecting rods or an undesirably high deflection oflevers is prevented.

Therefore, in the sense of this invention, a weighing sensor is providedwhich advantageously has a monolithic construction. It is intended foruse in an electronic scale according to the principle of electromagneticforce compensation, wherein the weighing sensor features extensions inthree different directions X, Y, and Z. Also provided is anelectromagnetic force compensation system which comprises a coil, amagnet, or a part of a position detection system.

The weighing sensor here has a section of a stationary base element, towhich parallel guide elements are coupled that extend essentially alonga first direction X and guide a load receiver that can move in themeasurement direction (direction Y) relative to the base element. Here,at least one lever and at least one coupling element are provided as aseries of elements effectively connected one behind the other, whereinthe elements are constructed for transmission or conversion of a loadacting on the load receiver and for forwarding it to the forcecompensation system.

Here, at least one component of the force compensation system isarranged on a lever arm of the last lever in the direction of force flowof the elements connected in series.

In comparison with the weighing sensors known from the state of the art,the present weighing sensor according to the invention differs in thatthe load receiver has a stop in the Y direction or Z direction for thelast lever or for at least one component arranged on this lever, suchas, e.g., a compensation weight.

In the non-energized or overloaded state of the weighing sensor, thelast lever in the direction of force flow can be deflected too far if acorresponding stop is not provided as a travel limit. Instead ofproviding this stop on the stationary base according to the state of theart, it is now constructed in a space-saving and functional way directlyon the load receiver, with which the corresponding lever arm theninteracts according to the invention. Alternatively, a compensationweight arranged on the lever or another component can strike against theload receiver if the loading or load release of the weighing sensortriggers a corresponding movement.

In addition, this produces the advantage that the last lever, whichshould extend advantageously in the direction of the load receiver,requires no additional add-on parts or formations in order to interactwith a section projecting from the stationary base. Instead, the levercan be guided, for example, on a straight line in the direction of forceflow, further toward the load receiver in order to be secured there bymeans of a simple stop device. Neither a projecting stationary base norextremities nor special lever geometries to be provided on the leverespecially for the stop function are necessary. This advantageouslysimplifies the lever design and thus the weighing sensor.

According to another advantageous embodiment of the invention, it isprovided that the stop be formed by a stop part arranged indirectly ordirectly on the load receiver. Advantageously, this stop part is anelement which is to be fixed on the load receiver and which projects,for example, into the inner space of the weighing sensor, in order tolimit the movement of the last lever in the Y direction. Additionally oralternatively, according to the invention, this part or another stoppart can also prevent movement in the Z direction, if it is arranged ormounted suitably on the load receiver. According to the invention, thestop part should be capable of adjustment or calibration, in order toprovide the maximum deflection path of the lever or the componentscarried by it.

The stop part can also be mounted indirectly on the load receiver, inthat it is connected to the load receiver by means of another component,while this other component can also be used predominantly for adifferent purpose.

Another embodiment of the invention provides that the stop be formedindirectly or directly by at least one recess of the load receiver. Herethe last lever or a compensation weight arranged on this lever or one ofthe components of the force compensation system should project into orthrough the recess at least also for the purpose of the stop. The recesscan be an indentation in the load receiver or also an opening completelypenetrating through the load receiver.

While a stop part arranged on the load receiver was described above forrealizing the stop function, the last design can also manage withoutsuch a separate stop part, because the edge of the recess takes over thefunction of the stop part in this case.

Because the passage of individual components of the weighing sensorthrough a recess of the load receiver can be advantageous for variousreasons (better lever effect, improved accessibility), the simultaneoususe of the recess in the load receiver as a stop simplifies theconstruction of the weighing sensor in an elegant way.

According to the invention, it can involve one or several recesses,which advantageously pass completely through the load receiver. Forexample, a recess arranged in the center is possible, through whichpasses a lever section of the last lever also guided in the center. Thisrecess can in particular be designed symmetric to a plane running in theX-Y direction, wherein this should also include a recess that startsfrom the plane and extends toward both sides. Advantageously but notnecessarily, the plane divides the load receiver symmetrically.

Alternatively, recesses are also conceivable that pass through the loadreceiver spaced apart symmetrically from the center plane describedabove, wherein the last lever to be limited in its freedom of motion, orthe components carried by it, are then also advantageously dividedsymmetrically in order to project into the mentioned recesses.

However, the recess does not necessarily have to be arranged symmetricto the previously described plane, but instead an asymmetric arrangementof the recess in the load receiver is also conceivable, withcorresponding arrangement of the component to be protected. Theasymmetric lever guide and the resulting asymmetric arrangement of therecess in the load receiver can be useful especially for reasons ofspace, when it can have an especially compact construction due to theasymmetric form.

Finally, one or more recesses can involve the edge region of the loadreceiver, so that they are not completely enclosed by the material ofthe load receiver. In this case, the component projecting through therecess would be accessible laterally, which would produce, for example,an advantage in assembly. The production of such recesses can also berealized in a simple way.

In another advantageous embodiment of the invention, the compensationweight, which can interact with the load receiver as a stop, can beattached from the side of the load receiver facing away from the baseelement section. Thus, the compensation weight can be easily mounted oradjusted, which simplifies the overall use of the weighing sensor. Here,the spatial extension of the compensation weight can affect the freepath over which the last lever can travel. A compensation weight, forexample, with a larger extent in the Y direction, strikes against theinner sides of the recess earlier than a weight with a smaller extent inthis direction. Thus, by selecting the dimensions of the compensationweight, the maximum permissible excursion of the last lever or itscomponents can be fixed essentially independently of the shape of therecess, which is also simplified by the easy accessibility.

The compensation weight can be composed of several individual weights,which, in their sum, determine the total compensation weight. At leastone of these weights can have a rotationally symmetric construction,wherein, among these several compensation weights, optionally withdifferent forms, at least this one weight projects into the recess ofthe load receiver. For a similarly rotationally symmetric recess in theload receiver, through the shape of the compensation weight, thepermissible deflection in the Y or Z direction is set by the resultingannular space between the weight and recess.

The compensation weight can be used, in particular, for compensating aninitial load or also for reducing the influence of vibrations (e.g.,ground vibrations).

According to another advantageous embodiment of the invention, anadjustment is performed for targeted positioning of the center ofgravity formed by the one or more compensation weights or the lastlever. In particular, for moving weighing sensors, inertial forcesappear that can load, among other things, the bearing points of thelever. If the weighing sensor rotates, for example, about an axisparallel to the Y direction, then centrifugal forces are produced on thelast lever and the one or more compensation weights. These centrifugalforces must be absorbed by the bearing of the last lever. To preventsimultaneous bending moments within the lever, according to theinvention, the common center of gravity of the arrangement made from thecompensation weights or the last lever should be capable of adjustment.This can be realized in a simple case by an adjustment screw, whose owncenter of gravity is adjustable relative to the previously mentionedcomponents, so that the common inertial forces (from the adjustmentscrew and the previously mentioned components) can be equalized orcompensated for a moving weighing sensor with respect to a bearing pointof the last lever. In particular, an adjustment of the center of gravityin the Y or Z direction should be possible according to the invention.

According to the invention, the compensation weight can also be providedas an initial weight compensation.

Other advantageous embodiments emerge from the subordinate claims andfrom the detailed description and the single drawing.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE shows a weighing sensor in a schematic, perspectiveview according to one embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Depicted in the single FIGURE is a weighing sensor 1 in a schematic,perspective view. A section 2 of a base element, which is to bedesignated as a stationary base, here supports two parallel guideelements 4 and 5 that extend forward in the X direction toward a loadreceiver 6. A lever mechanism, which is not shown in more detail andwhich is arranged essentially between the load receiver 6 and the baseelement section 2, causes the transmission of the weight forceintroduced into the load receiver 6 in the Y direction.

A recess 30 is formed in the load receiver 6 through which a fewcomponents of the weighing sensor are to be seen. The lever arm 10 of alast lever 9 extends in the X direction from the section 2 into therecess 30. The last lever 9 carries a schematically shown component M,S, P of a force compensation system with which the deflection of thelever 9 is compensated in order to derive a measurement value from thisdeflection. The components M, S, P can also be arranged somewhatdisplaced into the interior of the weighing sensor 1. A compensationweight 14 can also be arranged on the lever arm 10 instead of or inaddition to the previously mentioned components.

The compensation weight 14 carries an adjustment device 18, which isconstructed as a screw and which shifts its center of gravity relativeto the lever 9 by means of a screwing motion in order to compensateinertial forces due to movements of the weighing sensor.

According to the invention, the load receiver 6 has a stop for the lastlever 9 or the components carried by it. For example, an upper stop part40 is shown which limits a pivoting motion of the lever 9 in the Ydirection. Here, the adjustment device 18 can interact with the stoppart 40, wherein, however, the stop can also be formed in an arbitrarilydifferent manner, and in particular, without integration of theadjustment device 18.

Alternatively or additionally, another stop part 45 can be provided thatlimits movement of the lever 9, or the components carried by lever 9, inthe Z direction. The wall of the recess 30 itself can also act as adirect stop surface. Between the components 14, M, S, P on one side andthe stop part 45 there is actually a spacing. This spacing, althoughapparent from this description, is obscured somewhat in the figure dueto the perspective of the figure.

In the Figure, the arrangement of the stop part (40, 45) in the interiorof the recess 30 is shown. However, the stop part can also be arrangedon the inside or outside of the load receiver 6.

As used herein, the terms “comprising,” “including,” “having,”“containing,” “involving,” and the like are to be understood to beopen-ended, that is, to mean including but not limited to.

The above described preferred embodiments are intended to illustrate theprinciples of the invention, but not to limit the scope of theinvention. Various other embodiments and modifications to thesepreferred embodiments may be made by those skilled in the art withoutdeparting from the scope of the present invention.

1. A weighing sensor for an electronic scale according to the principleof electromagnetic force compensation, with elements that extend in afirst direction (X), a second direction (Y) perpendicular to the firstdirection, and a third direction (Z) perpendicular to the directions (X)and (Y), with at least one electromagnetic force compensation systemthat comprises a coil (S) or a magnet (M) or a part of a positiondetection system (P), the weighing sensor further comprising: a) astationary base element section to which parallel guide elements arecoupled that extend essentially along the X direction and guide a loadreceiver moving in the Y direction relative to the base element; b)wherein at least one of one or more levers and at least one of one ormore coupling elements are provided as a series of elements effectivelyconnected one behind the other, and wherein the series of elements areconstructed for the transmission or conversion of a load acting on theload receiver and for passing the load on to the electromagnetic forcecompensation system; c) wherein components of the electromagnetic forcecompensation system (M, S, or P) are arranged on a lever arm of aselected last lever of the one or more levers; and d) wherein the loadreceiver has a stop in the Y direction or in the Z direction for theselected last lever of the one or more levers or for at least onecomponent arranged on the selected last lever.
 2. The weighing sensor ofclaim 1, wherein the stop is formed by a stop part arranged indirectlyor directly on the load receiver.
 3. The weighing sensor of claim 1,wherein the stop is formed indirectly or directly by at least one recessof the load receiver, wherein the selected last lever, or a compensationweight arranged on the selected last lever, or one of the components (M,S, or P) also projects into or through the recess for the purpose ofstopping.
 4. The weighing sensor of claim 3, wherein the one or morerecesses have a symmetric or asymmetric construction relative to animaginary plane dividing the load receiver in the X-Y direction.
 5. Theweighing sensor of claim 3, wherein the one or more recesses are notclosed.
 6. The weighing sensor of claim 1, wherein a compensation weightis attached to the selected last lever of the one or more levers as astopping component on the side of the load receiver facing away from thebase element section.
 7. The weighing sensor of claim 1, wherein acompensation weight projects as a stopping component into a recess ofthe load receiver.
 8. The weighing sensor of claim 1, further includingan adjustment device for selective positioning of a common center ofgravity of the selected last lever, and the at least one componentcarried by the last lever.
 9. The weighing sensor of claim 1, wherein acompensation weight is provided as an initial weight compensation. 10.The weighing sensor of claim 1, further including a compensation weightwhich has a rotationally symmetric construction.
 11. The weighing sensorof claim 1, wherein the weighing sensor is a monolithic weighing sensor.12. An electronic scale according to the principle of electromagneticforce compensation, with elements that extend in a first direction (X),a second direction (Y) perpendicular to the first direction, and a thirddirection (Z) perpendicular to the directions (X) and (Y), with at leastone electromagnetic force compensation system that comprises a coil (S)or a magnet (M) or a part of a position detection system (P), theelectronic scale including a weighing sensor further comprising: a) astationary base element section to which parallel guide elements arecoupled that extend essentially along the X direction and guide a loadreceiver moving in the Y direction relative to the base element; b)wherein at least one of one or more levers and at least one of one ormore coupling elements are provided as a series of elements effectivelyconnected one behind the other, and wherein the series of elements areconstructed for the transmission or conversion of a load acting on theload receiver and for passing the load on to the electromagnetic forcecompensation system; c) wherein components of the electromagnetic forcecompensation system (M, S, or P) are arranged on a lever arm of aselected last lever of the one or more levers; and d) wherein the loadreceiver has a stop in the Y direction or in the Z direction for theselected last lever of the one or more levers or for at least onecomponent arranged on the selected last lever.
 13. The electronic scaleof claim 12, wherein the stop is formed by a stop part arrangedindirectly or directly on the load receiver.
 14. The electronic scale ofclaim 12, wherein the stop is formed indirectly or directly by at leastone recess of the load receiver, wherein the selected last lever, or acompensation weight arranged on the selected last lever, or one of thecomponents (M, S, or P) also projects into or through the recess for thepurpose of stopping.
 15. The electronic scale of claim 14, wherein theone or more recesses have a symmetric or asymmetric constructionrelative to an imaginary plane dividing the load receiver in the X-Ydirection.
 16. The electronic scale of claim 14, wherein the one or morerecesses are not closed.
 17. The electronic scale of claim 12, whereinthe compensation weight can be attached to the selected last lever ofthe one or more levers as a stopping component on the side of the loadreceiver facing away from the base element section.
 18. The electronicscale of claim 12, wherein a compensation weight projects as a stoppingcomponent into a recess of the load receiver.
 19. The electronic scaleof claim 12, further including an adjustment device for selectivepositioning of a common center of gravity of the selected last lever,and the at least one component carried by the last lever.
 20. Theelectronic scale of claim 12, wherein a compensation weight is providedas an initial weight compensation.